The present invention relates generally to a vortex-shedding bluff body, and more particularly to such a body having a minimal downstream extension, usable in a narrow profile flowmeter configuration.
It is well known that the presence of a bluff, or nonstreamlined, body within a moving fluid stream causes vortices to be shed alternately from opposite sides of the body, the frequency of production of the vortices being related to the flow rate of the fluid. The dynamics of the so-called Von Karman vortex street which emanates from the bluff body have been extensively studied, and the principles have been effectively applied in numerous commercial flow-rate measuring devices.
Although a single thin, flat plate is recognized as being capable of shedding vortices (see, for example U.S. Pat. No. 3,116,639), this shape has seen limited commerical use. Bluff bodies typically used in commerical flow meters have a more complex structure, and a downstream length which is a substantial fraction of the transverse width, generally resulting in a flowmeter of considerable length. For example, U.S. Pat. No. 3,572,117 shows a bluff body which extends downstream for a distance of one to two times its width. Similarly, in U.S. Pat. No. 3,948,097 the bluff body has a downstream length between 0.5 and 0.9 times its width, while U.S. Pat. No. 3,810,388 teaches that a width-to-length ratio of 1.5 (i.e., the length is 2/3 the width) yields maximum energy for vortex formation.
U.S. Pat. No. 4,297,898 discloses the use of "plate-like" upstream and downstream obstacles but the thickness of the respective obstacles and the gap therebetween yields a configuration whose overall downstream length is on the order of 1.2 times its width.
The use of a bluff body of appreciable downstream length has restricted the utility of a vortex flowmeter in certain applications. For example, a user of a narrow-profile flowmeter, such as an orifice plate, generally cannot replace his existing installation with the higher-performance vortex flowmeter without extensive modification to the piping system to accommodate the considerably longer vortex flowmeter housing. Although in U.S. Pat. Nos. 4,171,643 and 4,186,599 a narrow-profile vortex shedding configuration is formed from a thin plate, multiple vortex-shedding members are employed, spaced transversely across the diameter of the pipe.
In view of the above, it is an object of the present invention to generate strong, linear vortex streets from a bluff body without the need for a minimum downstream length. It is a further object of the invention to provide a narrow-profile vortex flowmeter using such a bluff body which is suitable for replacement of an orifice plate flow measuring system.